8128

• UCREFRP Catalog Number: 8128
• Author: U.S. Bureau of Reclamation.
• Title: Operation of Glen Canyon Dam\
• USFW Year: 1995.
• Copyright Material: NO

Description of Alternatives
From 1966 to 1989, annual releases ranged from 8.23 maf to 20.4 maf
(1984). The minimum release has occurred in about half the years since the
dam was closed in 1963.
Monthly Release
Volume Under the No Action Alternative, the volume of water released from Lake
Powell each month depends on forecasted inflow, existing storage levels,
monthly storage targets, and annual release requirements. Demands for
electrical energy, fish and wildlife needs, and recreation needs also are
considered and accommodated as long as the risk of spilling and storage
equalization between Lakes Powell and Mead are not affected. Power
demand is highest during winter and summer months, and recreation
needs are highest during the summer. Therefore, higher volume releases
are scheduled during these months whenever possible to benefit these
uses.
Spills are excess annual releases that cannot be used for project purposes;
they usually are the result of inflow forecast changes. Floodflows-the
spills of principal concern-are releases greater than the designed
powerplant capacity that are discharged through the river outlet works
and spillways.
Each month during the inflow forecast season (January to July), the
volume of water to be released for the rest of the year is recomputed based
on updated streamflow forecast information. Scheduled releases for the
remaining months are adjusted to avoid anticipated spills and maintain
conservation storage in accordance with the Long-Range Operating
Criteria.
Under high storage conditions, fall and early winter releases are designed
to meet the January 1 storage target (22.6 maf). Under lower storage
conditions, releases are scheduled at a minimum of about 550,000 acre-feet
per month. January through July releases are scheduled to create space in
the reservoir so that forecasted runoff will not produce spills but will fill
the reservoir in July. July through September releases are used to meet
both the minimum annual release requirement and the January 1 target of
22.6 maf.
Floodflow
Avoidance Methods for providing protection against flood releases under the
No Action Alternative are:
1. Storage in Lake Powell is not allowed to exceed 22.6 maf as of
January 1 of each year (before the forecast season) in preparation for
storing and regulating spring runoff.
18 Glen Canyon Dam EIS Summary